Effect of wettability of shale on CO2 sequestration with enhanced gas recovery in shale reservoir: Implications from molecular dynamics simulation

Abstract

The wettability of rock affects the interaction between CO₂, brine, and shale formation, which affects CO₂ sequestration with enhanced gas recovery (CS–EGR) project. However, under reservoir conditions, there is limited research on the surface wettability of shale organic matter, and its internal interaction mechanism is unclear. In this study, the effects of temperature, pressure, mineralization, and concentration ratio of CO₂ to CH₄ on the contact angle were studied using molecular dynamics (MD), and the results were compared with the previous experimental data. Under a certain pressure, the water wettability increases with the increase in temperature. At a fixed temperature, the contact angle of water on graphene increases with the increase of CO₂ pressure. Above the critical pressure, water at different temperatures is wetted by CO₂ on the surface of graphene, and the wettability reversal occurs. The water wettability decreases with the increase in solution salinity. Under the same concentration of droplets, Mg²⁺ and Ca²⁺ have a greater effect on the wetting angle than Na⁺. The adsorption capacity of the graphene surface for CO₂ is stronger than that of CH₄. Finally, the order of wettability is verified by interaction energy. This study will contribute to alleviating the greenhouse effect.